As an example of a conventional technology, Wideband Code Division Multiple Access (WCDMA) of the 3rd Generation Partnership Project (3GPP) Frequency Division Duplex (FDD)) standard is explained.
According to V3.12.0 applicable to Release 99 of a Nonpatent Literature 1 described below, the conventional CDMA radio communication system is optimized for a channel that requires real-time communication such as a sound channel. Concerning data communication, a High Speed Physical Downlink Shared Channel (HS-PDSCH) is provided in V5.5.0 applicable to Release 5 to realize improvement of throughput. For Radio Resource Control (RRC) between a base station control apparatus and a mobile apparatus, a channel of Release 99 called an Associated Dedicated Physical Channel (A-DPCH) is used.
Transmission power control for the channel of Release 99 is explained. A transmission slot in a base station includes a data section for transmitting sound and packets, a transmission power control (TPC) that is a type of a control signal of the layer 1 and used for transmitting a transmission-power control command, a Transport Format Combination Indicator (TFCI) that is a type of a control signal of the layer 1 and is used for channel coding/decoding, and a Pilot that is data of a known sequence and is used for synchronization and demodulation on a reception side. A transmission slot in a mobile apparatus includes a TPC, a TFCI, and a Pilot. A channel that transmits control information of the layer 1 such as the TPC, the TFCI, and the Pilot is referred to as a Dedicated Physical Control Channel (DPCCH).
As indicated by an example described in Annex.B B.2 of the Nonpatent Literature 1, the mobile apparatus estimates a quality of a Pilot signal transmitted by the base station. If the quality is lower than a reference value, the mobile apparatus transmits a transmission-power control command for instructing an increase of the next transmission power to the base station. If the quality is equal to or higher than the reference value, the mobile apparatus transmits a transmission-power control command for instructing a decrease of the next transmission power to the base station. The base station measures a Signal to Interference Ratio (SIR) of the Pilot signal transmitted by the mobile apparatus. If the SIR is lower than the reference value, the base station transmits a transmission-power control command for instructing an increase of the next transmission power to the mobile apparatus. If the SIR is equal to or higher than the reference value, the base station transmits a transmission-power control command for instructing a decrease of the next transmission power to the mobile apparatus.
According to a Nonpatent Literature 2 described below, the reference value is called a “UL SIR Target” and is designated by information of a control protocol called a Node B Application Part (NBAP) by the base station control apparatus. According to a Non-patent Literature 3 described below, it is possible to change the reference value according to an “OUTER LOOP POWER CONTROL message” in a protocol called “fp:frame protocol”.
It is known that, as described in a Patent Document 1 described below, the channel of Release 99 is set to low transmission power to reduce unnecessary waves at the beginning of setting of new communication. When the transmission power becomes stable, the channel is controlled to perform transmission with transmission power selected based on a line quality condition set in advance. For example, a line quality is defined as Frame Error Rate (FER)=0.01 for a sound line and FER=0.0001 for 64 kbps data. The line quality is controlled to set the FER to a target value to guarantee a quality for end users. To attain an identical line quality, as an index such as a Signal to Interference Ratio (SIR), a Signal to Noise Ratio (SNR), a Signal to Interference plus Noise Ratio (SINR), or reception field intensity, different values are required according to propagation environments.
The conventional transmission power control at the time when there is no data to be transmitted will be explained. In the 3GPP-FDD standard, even when there is no data to be transmitted in the data section (amplitude=0), transmission processing is performed in the DPCCH. However, there is no particular description about transmission power of the DPCCH.
For example, as the conventional technology at the time when there is no transmission data, there is a technology described in a Patent Document 2 described below. In the Patent Document 2, when transmission data is absent, a burst frame consisting of only burst data including a pilot symbol and a symbol for transmission power control is generated and a transmission interval is set to N times (N is a natural number) as large as one slot. Consequently, the DPCCH is not transmitted for every slot but is transmitted once in N slots. When a transmission amplifier of the mobile apparatus is turned off in slots in which the DPCCH is not transmitted, power consumption can be reduced.
It is also mentioned that data subjected to repetition processing is transmitted with transmission power lower than that before the processing by providing repetition processing means for continuously arranging pilot symbols and symbols for transmission power control, respectively. A repetition technology for changing a format of transmission and repeatedly transmitting the same data is used to reduce the transmission power by × dB.
Patent Document 1: Japanese Patent Application Laid-open No. 2000-91985
Patent Document 2: Japanese Patent Application Laid-open No. H11-41203
Nonpatent Literature 1: TS25.214 “Physical layer procedures (FDD)”
Nonpatent Literature 2: TS2.5.433 “UTRAN Iub Interface NBAP signaling” 9.1.36, 9.1.42
Nonpatent Literature 3: TS25.427 “UTRAN Iub/Iur interface user plane protocol for DCH data streams” 6.3.3